1. Field of the Invention
The present invention relates to a multi-layered optical disk including two or more recording layers, and an optical disk device capable of addressing a focus lead-in operation into the multi-layered optical disk.
2. Description of the Related Art
In recent years, the so-called multi-layered optical disks have been proposed for the purpose of enhancing recording capacities of optical disks. Here, each of these multi-layered optical disks is implemented by providing a plurality of recording layers within a piece of optical disk. An example of these multi-layered optical disks is a 100-GB multi-layered optical disk that is implemented by multilayering four recording layers each of which is a 25-GB recording layer.
A shortening of the set-up time is regarded as one of performances requested for an optical disk device for performing reproduction or recording of data with respect to these multi-layered optical disks. The set-up time refers to a time which elapses from a point-in-time when a user installs an optical disk into the optical disk device to a point-in-time when the user becomes capable of executing the reproduction or recording of data. The shorter this set-up time becomes, the higher the user convenience becomes.
In general, an optical disk device is requested to exhibit the downward compatibility which allows the optical disk device to address the CDs and DVDs, i.e., the conventional optical disks. In response to this request, the optical disk device performs a disk judgment processing for judging the type of an optical disk installed therein. The operation of the disk judgment processing is as follows: The installed optical disk is irradiated with a laser light. Moreover, a basic judgment operation for the disk type, i.e., CD, DVD, or BD, is performed, using the level of a reflected light from the optical disk. Incidentally, in this basic judgment operation, if the disk type has been successfully judged to be, e.g., BD, it is difficult to accurately distinguish among more detailed types such as BD-ROM, BD-R, and BD-RE. Even if the judgment on the more detailed types has been successfully made, there is a possibility of the false judgment. Accordingly, the optical disk device is required to perform the following operation: The optical disk device performs the focus lead-in operation into the installed optical disk. After that, the device reproduces control information recorded into the optical disk in advance. Furthermore, based on disk type information included in the control information reproduced, the device clarifies and confirms the type of the installed optical disk ultimately.
Also, the control information includes therein respective types of information for controlling the optical disk device. Example of the respective types of information are such information as polarity of a push-pull signal and polarity of a RF signal. The optical disk device is required to appropriately set respective types of circuits within the device in accordance with the above-described respective types of information.
From the foregoing explanation, implementation of the shortening of the set-up time requires that the control information recorded in the optical disk be reproduced swiftly. This requirement makes it desirable to swiftly perform the focus lead-in operation into a recording layer where the control information is recorded.
In, e.g., JP-A-2004-152398, the following multi-layered optical disk is disclosed for the purpose of performing the focus lead-in operation into a recording layer where the control information is recorded: Namely, in this optical disk, of a plurality of recording layers, a lead-in area is provided only in a predetermined recording layer. Simultaneously, at the radius position at which the lead-in area is disposed, the other recording layers possess no reflection layers. In the multi-layered optical disk disclosed in JP-A-2004-152398, as is the case with the conventional single-layered optical disks, it is possible to perform the focus lead-in operation at the radius position at which the lead-in area is provided. This condition allows the optical disk device to easily perform the focus lead-in operation into the recording layer where the lead-in area is provided, thereby making it possible to swiftly reproduce the control information recorded in the lead-in area.
Also, in general, when the recording layer of an optical disk becomes multi-layered, it becomes difficult to record the control information into a predetermined recording layer with a high accuracy. In JP-A-2007-66489, in order to solve this problem, the following multi-layered optical disk is disclosed: Namely, in this optical disk, of a first recording layer including a control-information recording area where the control information is recorded, and another recording layer, at least either of the recording film and the reflection film of another recording layer is formed in a manner of avoiding the control-information recording area. This configuration makes it possible to record the control information with a high accuracy.